(a) Field of the Invention
This invention relates to 3-substituted phenyl-2-isoxazoline-5-carboxylic acid and their esters, and plant growth regulators containing the same, more particularly, growth inhibitors and sterilizing agents and to a method for regulating the plant growth by applying the same.
(b) Description of the Prior Art
The plant growth regulators are organic compounds produced in the plant body and control physiological function such as growth, vegetation, organogenesis and the like by migrating through the plant body. These growth regulators are also chemical substances which may be referred to as plant hormones exhibiting their activity in trace amounts, synthetic materials having activity equivalent to these hormones or antiplant harmones having antagonism to these hormones and materials. The plant growth regulators which are currently in practical use include germinating accelerators, rooting accelerators, fruit thinning agents, fruit-drop regulators, growth inhibitors, self-fertiliging agents and the like. The activity, however, is not sharply differentiated but appeared in combination. The emerging activity remarkably varies according to concentration of treatment, growth stage of the plants, part of the plant treated, and the like. For example, 2,4-D (2,4-dichlorophenoxyacetic acid) which is used as a herbicide is also employed for a germinating and rooting agent in a low concentration, and gibberellin which is a phytohormone to accelerate the plant growth is also used as the self-fertilizing agent.
In this invention, the term "growth inhibitor" refers to an agent which creates a stout plant form with a low height by specifically retarding the intermode growth of stalks without affecting the growth of foliage and roots. Crops having such plant form can maintain stable yield of harvest as a result of less break or fall due to a strong wind such as a typhoon etc. Reaping operation of these crops also becomes easier in harvest time. Besides the nutrients which are to be used for the growth are utilized in the edible parts of the plants and thus increase the amount of harvest. Furthermore, trimming operations of turfs can be reduced in parks and golf courses. These effects lead to a remarkable advantage. At present, CCC (2-chloroethyltrimethylammonium chloride) and B-Nine (N-dimethylaminosuccinamic acid) are used as the growth inhibitors and yet restricted to horticultural plants and wheat. Therefore it has been desired to provide highly active growth inhibitors which can be employed for a wide range of crops.
The sterilizing agents may be used for proliferation inhibition of noxious weeds by retarding seminal formation and yet none of them has been known in practical use.
Japanese Patent Laid-open Publication No. 88591/1980 (see also European Published Patent Application No. 0013111) discloses herbicidal activity or growth retarding effect of spiro derivatives of 3-aryl-2-isoxazoline.
Japanese Patent Laid-open Publication Nos. 88591/1980 and 113772/1980 (see also U.S. Pat. No. 4,197,405) disclose examples for applying the above-described spiro derivatives to the preparation of 2-(3-aryl-5-isoxazolyl)benzoic acid derivatives which are useful as the herbicides. In addition, Japanese Patent Laid-open Publication No. 137472/1984 [see also Chemical Abstracts, 102, 24614d, (1985)] discloses examples of employing 3-trifluoromethyl-2-isoxazoline derivatives as intermediates for the preparation of 3-trifluoromethylisoxazole derivatives which have antibacterial activity. Any of the above-described examples however, are limited to utilization as the intermediates.
A new synthetic method of 2-isoxazoline derivatives has been described in Tetrahedron Letters, 25, 2029-2030 (1984) and related compounds of this invention such as methyl 2-(4-chlorophenyl)-2-isoxazoline-5-carboxylate have been written in the examples. No description, however, has been found on their properties and no reference has also been made concerning their physiological effect.